Camera modules of this type installed in vehicles serve to record the surroundings of the vehicle in order to be able to use the image data for numerous functions, such as lane detection, traffic sign recognition, high-beam assistant, collision warning, pedestrian detection, etc., wherein the analyzed image data is also used as a basis for intervening in vehicle control systems, e.g. braking or engine controls. If such camera modules are to be used a fixed-focus camera system in driver assistance systems, it is crucial that they have a certain quality with regard to focusing and tilting.
In general, these camera modules have a structure consisting of a printed circuit board which serves as a support plate and on which an image sensor is mounted, and an optical system fixed thereto. The objective lens of the optical system is either held in place by an objective lens holder or fixed directly to the support plate.
To focus the optical system, a fixing solution is required which enables the distance between the optical elements of the optical system and the image sensor to be adjusted. In the simplest case, this is done by means of a screw thread. The drawback of this is that only one adjustment along one axis is possible in this way.
To be able to adjust several axes, an adhesive connection is often the method of choice. To focus the camera module, a structure is mostly selected where a target on which said module is to be focused is positioned at a defined distance in front of the camera module. In this adjustment structure, the image sensor is operated, and the position of the optical system is moved after the adhesive has been applied. The sequence of images taken during the movement process can be used to determine the best focus position of the optical system. To determine this point of best focus, sharpness values of the images taken at the different positions are recorded in a diagram and used to determine a sharpness curve. The local maximum of this sharpness curve indicates the best focus position as a function of the distance from the target. By making a defined addition to this position, the structure and method described above can also be used to set the focus to a distance other than the target distance. Once the focus position has been adjusted, the adhesive is cured, thus securing the adjustment.
However, this method has the following drawbacks, which are in particular due to the adhesive connection:                An electrical connection between the support plate and the processing unit of the camera module is required. If the optical elements are held at the objective lens, a certain force is exerted on the adhesive connection regardless of how the electrical connection is designed. Therefore said adhesive connection must be adapted to the forces that may occur.        The adhesive is often cured using UV light and/or heat. The time taken for the adhesive to cure very often predetermines the cycle time for the production of such a camera module. This entails long production times and hence high manufacturing costs, and        The adhesive connection must be stable over a long time in different environmental conditions, in particular in the automobile sector. In this context, attention must be paid to the weight of the optical system and the support plate, in particular due to mechanical shock and vibration.        
The last-mentioned drawback is avoided in a known camera module according to DE 10 2011 011 527 A1, which is incorporated by reference by providing a shared module housing for the optical system and the image sensor, wherein a printed circuit board on which the image sensor is mounted can be inserted into the module housing and arranged and aligned accurately behind the optical elements within the module housing through engagement and adjustment openings, and wherein the printed circuit board with the image sensor is connected to the module housing by means of an adhesive connection in order to allow for focus adjustment. Compared to a prior-art assembly, this adhesive connection only needs to carry the weight of the printed circuit board with the image sensor.
From DE 10 2005 006 756 A1, which is incorporated by reference a camera module is known where no adhesive connection between a support carrying a printed circuit board on which an image sensor is mounted and an optical system or a camera housing is provided to allow for focus adjustment. To focus-adjust the image sensor, the support can be moved within a housing of the camera module along several axes, so that the support can be fixed in place using mechanical fixing means, e.g. screws, once an optimum adjustment position has been reached. However, for the support to be movable, much assembly work is required, resulting in high manufacturing costs of the camera module.